Oxidation resistant hydraulic oil



United States Patent Otlice 3,2 74 ,1 l3 Patented Sept. 20, 1966 This invention relates to hydraulic fluids and more particularly to hydraulic oils having improved oxidation resistance characteristics.

Oxidation stability is one of the most important properties of hydraulic oils. The term oxidation stability, as applied to hydraulic oils, means that the oil does not become non-operational in a hydraulic system after a reasonable period of time even though certain difierenccs in the oil properties resulting from oxidation have occurred.

Resins and other oxidation products begin to form almost immediately after an oil is put in use; the rate of formation can be extremely low or exceedingly high, depending on the oil and operating conditions. Certain resins which are formed are soluble in the oil. This formation causes a darkening in color (not inherently an undesirable property) and an increase in viscosity of the oil. When the resins come in contact with very hot surfaces there is a tendency for some types to be changed into insoluble compounds that may either bake out on the hot surface or circulate as solids suspended in the oil. In the form of hard dark coatings, such products are called varnishes or lacquers; other forms, which often settle out at some low point in a hydraulic system, are called sludges. Frequently, these sludges, together with small bits of metal, and other types of dirt, form even more obje'ction able mixtures that might be called super-sludges.

Obviously, a high rate of oxidation cannot be tolerated in a hydraulic system because the products of oxidation clog small orifices, tend to jam tightly fitted parts, and destroy the whole balance of the system. Moreover, since products of oxidation are acidic, they are likely to attack metal parts and thus destroy precisely machined surfaces.

The problem of oxidation stability of hydraulic oils has been widely recognized in the prior art. A great number of attempts to overcome this problem have been tried. Since oxidation stability of hydraulic oils is of such great importance, numerous evaluation methods thereof have been developed. The most widely used and accepted method for testing oxidation resistance of hydraulic oils is ASTM D-943. Even though no test has yet been devised that will positively demonstrate Whether or not a hydraulic oil will resist oxidation to an acceptable degree, it has been shown that if an oil tests poorly in ASTM D943, it Will probably perform less than satisfactorily under rigorous operating conditions.

According to ASTM D-943, 60 ml. of water are added to 300 ml. of the oil to be tested. The mixture is maintained at about 205 F. in the presence of a copper-iron catalyst while oxygen is bubbled through the oil-water mixture at a constant rate. Periodically the extent of oxidation is determined by testing for neutralization numher. The test is considered finished when the neutralization number of the oil has a value of 2.0. The time, in hours, needed to reach this value is taken as a measure of the relative resistance of the oil to oxidation. In general, prior art hydraulic oil compositions fail the D-943 test at between 1000 and 2000 hours.

A composition has now been found which when subjected to the D-943 test has a rating of from 2-4 times subjected to vacuum fractional distillation.

the number of hours as heretofore acceptable prior art hydraulic oil compositions.

The novel composition of this invention comprises a major amount of amineral oil, and minor amounts of (a) A hindered phenol having the general formula I OH wherein R and R are alkyl radicals containing from 1 to 8 carbon atoms,

(b) An oil soluble alkylated succinic anhydride having the general formula R-CH-C=O CH2(I]=O wherein R is an alkyl radical containing from 6 to 20 carbon atoms, and

(c) A material selected from the group consisting of an aromatic secondary amine, a sulfurized terpene and a 1,3,4-thiadiazole polysulfide.

The mineral oil component comprising the major proportion of the composition of this invention is any refined mineral oil and is preferably a solvent refined paraffinic oil. Such oils are prepared by a variety of processes. For example a particularly preferred oil which can be used in this invention is obtained by first subjecting a parafiinic crude oil to distillation under atmospheric pressures. There is obtained a long residue which is a fraction which does not distill under the conditions used without undue decomposition. The long residue is then subjected to steam distillation, usually under a vacuum. Under these conditions gas oil and waxy lubricant fractions distill over leaving a bottoms which is conventionally termed a short residue or a steam refined stock also known as a cylinder stock. The distillate and bottoms fractions are then solvent extracted with furfural and a countercurrent propane-cresylic acid system respectively. The separate raflinates typically have the physical properties as set forth in Table I.

Table I Furfural ratlinate Propane-cresylie acid ratfinate ASTM D4160:

Init., F 584 713 10 712 801 770 919 854 854 1, 030

40 r, Color, ASTM D1500 0.5 5. 5

After solvent extraction, the separate rafiinates are combined and solvent dewaxed with a suitable solvent such as methyl ethyl ketone by methods which are well known in the art. The dewaxed product is conventionally known as a total pressed oil. The total pressed oil is then Three separate distillate fractions and a bottoms material are recovered. The bottoms is commonly known as a bright stock. Typical properties for the total pressed oil and the distillate fractions are set forth in Table II.

Table II Prgssled Fraction 1 Fraction 2 Fraction 3 Bright Stock ASTM D-1160:

Init., F 601 654 755 773 910 699 789 867 993 743 842 957 807 910 1, 024 827 923 1, 030 1, 030 31. 9 30. 4 29. 3 26. 4 112 210 515 2, 775 40. 2 46. 7 63. 1 155 r, F 0 0 0 Color, ASTM D-1500 L1. 0 L1. 5 L2. 0 L6. 5

The hindered phenols are used in the novel composition of this invention in an amount in .the range of from 0.1 to 2.0 preferably 0.2 to 1.0 percent by weight. As stated above these compounds have the following general formula wherein R and R are alkyl radicals containing from 1 to 8 carbon atoms. It is preferred that at least one of the alkyl radicals be of branched configuration. Examples of suitable substituted phenols which can be used in this invention include 2,4,6-trimethylphenol; 2,6-ditertiarybutyl-4-rnethyliphenotl; 2, 6 dineopentyl-4-methylphenol; 2-ethyl-4-methyl-o-t-butylphenol; 2 isopr-opyl-4-methyl- 6-neopentylphenol, etc. The most preferred hindered phenol to be used in this invention is 2,6-ditertiarybutyl- 4-methylphenol.

The oil soluble a'l kylated sucoinic anhydrides used in this invention are present in an amount in the range of from 0.001 to 0.5 preferably 0.005 to 0.05 percent by weight. As stated above, these compounds have the general formula wherein R is an alkyl radical containing from 8 to 20 carbon atoms. Examples of suitable alkylated succinic anhydrides which can be used in this invention include the isomeric octyl swccinic anhydrides, nonly succinic anhydrides, decyl succinic anhydrides, dodecyl succinic anhydrides, pentadecyl :succinic anhydrides, etc. The most preferred alkyl succinic anhydrides to be used in this invention are those in which the alkyl radical contains at least 12 carbon atoms.

wherein R and R are selected from the group consisting of hydrogen and an alkyl radical containing from 1 to 20 carbon atoms. Examples of suitable amines which 'can be used in this invention include diphenylamine; ethylphenylamine, N-phenyl-; t-butylphenylamine, N- phenyl-; di(hexylphenyl)amine; hexylphenylamine, N-tbutylphenyl-; di(octylphenyl) amine; dodecylphenylaminm,

N-octylphenyl-; etc. The most preferred amines to be used in this invention are the isomeric di(octylphenyl) amines.

Sulfurized terpenes are well known. Those which can be used in this invention are oil soluble and can be prepared by any of the accepted methods of sulfurizing unsaturated hydrocarbons. Among the sulfurization processes which can suitably be employed is that of treating the terpene with sulfur and hydrogen sulfide in the presence of water or steam at temperatures within the range of about 250 F. to 450 F. and at pressures up to about 1500 pounds per square inch for a period of 1 to 10 hours. The sulfurized terpene can also be prepared by treating the desired terpene with a sulfur chloride, such as S Cl or SCl at a temperature within the range of about 60 F. to about 250 F. When the terpene is sulfurized with a sulfur chloride, the chlorine present in the sulfurized material can be removed by treating the sulfurized material in a bomb at a temperature of about 300 F. to about 400 F. with ammonia or other aqueous or alcoholic alkalies, alkali metal sulfides and polysulfides, such as a sodium sulfide, or other bases. The sulfurized terpenes which are best suited or use in the instant invention are those which have a sulfur content of from about 5% to about 45%. Among the particular compounds found suitable for the purposes of the invention are the oil-soluble sulfurized derivatives of terpinolene; alpha, beta and gamma terpinene; limonene; dipentene; alpha and beta phel landrene; sylvestrene; carvestrene; methene; carvomenthene; and isomers thereof.

The 1,3,4-thiadiazole polysulfides useful in this invention have the general formula wherein R and R are the same or different hydrocarbon radicals, x and y are numbers 0 to about 8, the sum of x and y is at least 1, and preferably 2 to about 16. The radicals R and R can be aliphatic or aromatic, including talkyl, aralkyl, aryl and talkaryl radicals. The acylic radicals, can contain from 2 to about 30 carbon atoms, and preferably from about 4 to about 16 carbons atoms. Examples of suitable hydrocarbon radicals are ethyl, propyl, butyl, hexyl, octyl, nonyl, decyl dodecyl, tridecyl, hexadecyl, octadecyl, cyclohexyl, phenyl, tolyl, benzyl, styryl, naphthyl, etc.

The polysulfide derivatives can be suitably prepared by several methods. For example, they can be prepared by reacting 2,5-dimercapto-1,3,4-thiadiazole with a suitable sulfenyl chloride, or by reacting the dimeroaptan with chlorine and reacting the result-ant disulfenyl chloride,

N N ClS(") -s-cr with a primary or tertiary mercaptan. Bis-trisulfide derivatives are obtained by reacting the dimercaptan with a mercaptan and a sulfur chloride in molar ratios of from 122:2 to 1:224 at a temperature of from about 50l00 C. Higher polysulfides can be prepared by reacting the thiadiazole dior trisulfides with sulfur at temperatures of about ZOO-400 F. Another method of preparing the polysulfides involves reacting 2,5-dimercapto-1,3,4- thiadiazole with a mercaptan and sulfur in the molar ratio of from 1:1:1 to 1:4:16 at temperatures of from about 75 C. to about 150 C.

To further illustrate the instant invention a number of different compositions were prepared using the abovenoted ingredients and tested according to ASTM D943. In the following tables all parts are by weight. The base oil was a blend of two fractions having the properties of Fractions 1 and 2 as set forth in Table II in a 45:55 ratio respectively.

CIR-(3:0 wherein R is an alkyl radical containing from 6 to carbon atoms, and (c) 0.001 to 2.0 Weight percent of an oil soluble material 0 selected from the group consisting of an aromatic secondary amine having the general formula 2,6-di-t-buty14-m ethylphen o1 Hexadecyl succinic anhydride Di(octylphcnyl) a1nine Sulfurized dipentene 2,5-dioctyldithiothiadiazole 1)943 hours In Table III it is clearly shown that a refined oil alone or in combination with any one of the additive components used in this invention is unacceptable as an oxida tion resistant hydraulic oil.

wherein R and R are selected from the group consisting of hydrogen and alkyl radicals containing 1 to 20 carbon atoms, a sulfurized terpene and a 1,3,4-thiadiazole polysulfide having the general formula Table IV G i H J K L M N Oil 99. 1 99. 99 4 99. 85 99. 65 99v 6 99. 65 2,6-di-t-butyl-4-methylphenol 0.6 0. 6 0 5 0. 1 Hexadecyl succinic anhydride 0. 03 0. 03 0. 03

Di(octylphenyl) amine. Sulfurized dipentene. -W 2,5-di0 etyldithiothiadiazol D-943 hours In Table IV it is apparent that some of the compositions would be somewhat acceptable as oxidation resistant hydraulic oils, but the majority of the compositions shown therein would be considered to have failed the D-943 test. wherein R and R are hydrocarbon radicals selected Table V O P i Q Oil 98. 7 99. 05 98. 2,G-di-t-buty1-4-methylphenol 0. 5 0. 6 0. Hexadecyl suecinic anhydride. 0. 03 0. 03 O. Di(octylphenyl)amine 0. 5 0. 05 0. Sulfurized dipentene I I i 2,5-dioctyldithiothiadiazolet D943 hours 3, 200 3, 950 3, 750

The data shown in Table V clearly demonstrate the synergistic action between the different additive components when incorporated into hydraulic oils in accordance with (a) 0.1 to 2.0 weight percent of a hindered phenol having the general formula R H-R' wherein R and R are alkyl radicals containing from 1 to 8 carbon atoms,

from the group consisting of ethyl, propyl, butyl, hexyl, octyl, nonyl, decyl, dodecyl, tridecyl, hexadecyl, octadecyl, cyclohexyl, phenyl, tolyl, benzyl, styryl, and naphthyl, and wherein x and y are integers in the range of from 0 to 8 and wherein the sum of x and y is at least 1 and ranges up to about 16.

2. The oxidation resistant hydraulic oil of claim 1 wherein said hindered phenol is present in an amount in the range of from 0.1 to 2.0 weight percent, said oil soluble alkylated succinic anhydride is present in an amount in the range of from 0.001 to 0.5 weight percent and wherein the oil soluble material is said aromatic secondary amine and which is present in an amount in the range of from 0.001 to 2.0 weight percent.

3. The oxidation resistant hydraulic oil of claim 1 wherein said hindered phenol is present in an amount in the range of from 0.1 to 2.0 weight percent, said oil soluble alkylated succinic anhydride is present in an amount in the range of from 0.001 to 0.5 weight percent and wherein the oil soluble material is said sulfurized terpene and which is present in an amount in the range of from 0.001 to 2.0 weight percent.

4. The oxidation resistant hydraulic oil of claim 1 wherein said hindered phenol is present in an amount in the range of from 0.1 to 2.0 weight percent, said oil soluble alkylated succinic anhydride is present in an amount in the range of from 0.001 to 0.5 weight percent and wherein the oil soluble material is said 1,3,4-thiadiazole polysulfide and which is present in an amount in the range of from 0.001 to 2.0 weight percent.

5. The oxidation resistant hydraulic oil of claim 1 wherein said hindered phenol is present in an amount in the range of from 0.2 to 1.0 weight percent, said oil soluble alkylated succinic anhydride is present in an amount in the range of from 0.005 to 0.05 weight percent and wherein the oil soluble material is said aromatic secondary amine and which is present in an amount in the range of from 0.005 to 0.2 Weight percent.

6. The oxidation resistant hydraulic oil of claim 1 wherein said hindered phenol is present in an amount in the range of from 0.2 to 1.0 weight percent, said oil soluble alkylated succinic anhydride is present in an amount in the range of from 0.005 to 0.05 weight percent and wherein the oil soluble material is said sulfurized terpene and which is present in an amount in the range of from 0.005 to 0.2 weight percent.

7. The oxidation resistant hydraulic oil of claim 1 wherein said hindered phenol is present in an amount in the range of from 0.2 to 1.0 weight percent, said oil soluble alkylated succinic anhydride is present in an amount in the range of from 0.005 to 0.05 weight percent and wherein the oil soluble material is said 1,3,4-thiadiazole polysulfide and which is present in an amount in the range of from 0.005 to 0.2 weight percent.

8. An oxidation resistant hydraulic oil comprising a major amount of a solvent refined paraifinic oil and from 0.2 to 1.0 weight percent of 2,6-ditertiarybutyl-4-methylphenol, 0.005 to 0.05 weight percent hexadecyl succinic anhydride and 0.005 to 0.2 weight percent 2,5-dioctyldithiothiadiazole.

9. An oxidation resistant hydraulic oil comprising a References Cited by the Examiner UNITED STATES PATENTS 2,459,717 1/1949 Perry. 2,877,184 3/1959 Ragborg 25278 2,913,415 11/1959 Schmitz 252-78 LEON D. ROSDOL, Primary Examiner.

ALBERT T. MEYERS, Examiner.

R. D. LOVERING, Assistant Examiner. 

1. AN OXIDATION RESISTANT HYDRAULIC OIL COMPRISING A MAJOR AMOUNT OF A MINERAL OIL AND (A) 0.1 TO 2.0 WEIGHT PERCENT OF A HINDERED PHENOL HAVING THE GENERAL FORMULA 